For example, a mounting-subject member such as a trim board cover is detachably mounted on a mount-base member such as a body panel of a vehicle. To detachably mount one member on the other member, a clip including a grommet and a pin is used.
Conventionally, as such clip, Patent Document 1 discloses a clip (an expansion type rivet for fastening overlapping plates) including a grommet (a female member) and a pin (a male member). The grommet has a collar, elastic leg pieces which extends from the collar while being divided via a cutout portion and which is adapted to flex and projections which project radially inwards from lower ends of the elastic leg pieces. The pin has a head portion, a shaft portion which extends from the head portion, an expansion portion which is formed at an axially intermediate position along the length of the shaft portion so as to expand the elastic leg pieces radially outwards and recess portions formed vertically in the expansion portion for accommodating and catching therein the lower ends of the elastic leg pieces.
Then, the pin is inserted into the grommet and the projections at the lower ends of the elastic leg pieces are brought into engagement with the recess portions at a proximal end portion side of the shaft portion, whereby the pin is held in the grommet so as not to be dislodged therefrom. With the pin kept in that state, when the clip is inserted into mounting holes of both members and the pin is pushed further into the grommet, the projections are pushed to be expanded from inside by the expansion portion so as to open the elastic leg pieces, whereby both the elastic leg pieces are brought into engagement with a circumferential edge on a backside of the mounting hole in one member, while the collar is brought into abutment with the other member, both the members being thereby coupled together via the clip.    Patent Document 1: JP-UM-H04-034507-A